Is she falling out of love?

My girlfriend and I have been dating for 3 years now. A foreign friend introduced us to each other during a party. I immediately liked her after our first encounter but she didn't notice me. I really took the effort to get her number, ask her out, etc. Eventually we got together and my years with her is honestly the best in entire life. Although, I can't help but notice that her attitude towards me seems different recently.

She has become less affectionate and less empathetic. She easily gets pissed at me and it seems like everything I do ticks her off. I tried asking her what was wrong but she would say I'm just overthinking. I'm afraid to ask if she still loves me because the answer might hurt me. I don't know what to do anymore